Method and apparatus for providing a spiral cut in small resistances



Dec. 12, 1961 E. H. LAYER, JR., ETAL 3,012,383

METHOD AND APPARATUS FOR PROVIDING A SPIRAL CUT IN SMALL RESISTANCESFiled Aug. 17, 1960 2 Sheets-Sheet 1 fiIl 23 l3 2 ll g F n E22 26 7 I8 i(n- 20 Dec. 12, 1961 E. H. LAYER, JR.. ETAL 3,012,383

METHOD AND APPARATUS FOR PROVIDING A SPIRAL CUT IN SMALL RESISTANCES 2Sheets-Sheet 2 Filed Aug. 17, 1960 ATTORNEY AGE NT United States Patent3,012,383 METHOD AND APPARATUS FOR PROVIDING SPIRAL CUT IN SMALLRESISTANCES Edwin H. Layer, J12, Columbus, Ohio, Earl R. Olson, PalosVerdes Estates, Calif., and Joseph 0. Morgan, Belleviile, Mich,assignors to the United States of America as represented by theSecretaryof the Air Force Filed Aug. 17, 1960, Ser. No. 50,299 Claims.(Cl. 51-259) This invention relates to a device for use when using alathe to provide a spiral cut in small resistances.

One object of the invention'is to provide a means for providing a spiralcut in a small resistance element which maintains a substantiallyconstant force on the resistance element during grinding.

Another object is to provide a device for use in providing a spiral cutin a small resistance element which will not produce excessively deepcuts or skipping.

These and other objects will be more fully understood from the followingdetailed description taken with the drawing, wherein:

FIG. 1 is a front elevational view of the device of the invention;

FIG. 2 is a side view of the device of FIG. 1;

FIG. 3 shows the device of the invention mounted in the lathe; and

FIG. 4 is a sectional view of the device of FIG. 1 along the lines 4-4,also showing the relative location of the grinding wheel of the lathe.

Prior art devices have not been able to control the forces on theresistor with sufficient accuracy to prevent excessively deep cuts orskipping due to slight misalignment of the chuck or slightly crookedbase rods. Various methods have been used for producing spiral cuts insmall resistors, but none of these have been entirely successful.Suspension of the entire grinding motor and spindle in a free swingingmount was found to be satisfactory when working with large resistorsizes but this method was found to be unsatisfactory for very smallresistors because the grinding force could not be accurately controlleddue to the excessive friction in the bearings and the large mass of theswinging mount combined with the lack of straightness in the rods.According to this invention, more sensitive control and greaterconstancy of the grinding force is provided with the use of alight-weight frame constructed to hold the resistor in a free swingingposition beneath the lathe spindle axis with rotation transmitted fromthe spindle to the resistor through spur gears. The frame is providedwih a spring loaded conical chuck to hold the resistor. A dash pot isprovided to damp out sudden changes in the position of the frame. Acounterweight arm is fastened to the. frame near the main axis of theunit to which weights are suspended to provide a substantially constantforce of the resistor against the grinding wheel.

Referring more particularly to FIG. 1 of the drawing, a frame has ashaft 11 supported in bearings 12 and 13, which is adapted to beconnected between the centers of a lathe. A chuck 14 connected to shaft15 is supported in bearing 16. A second chuck 17 connected to shaft 18is supported within bearing 19. Bearings 12, 13, 16 and 19 are miniatureprecision bearings which provide minimum friction. In operation, aresistor blank 29 is supported between chucks 14 and 17 and is held inplace by means of a spring 21. The assemblies 15, 14, 20, 17 and 18 aredriven by means of a pair of spur gears 22 and 23. While these gearshave been shown to be substantially the same size to provide the samerate of rotation for the resistor 20 as for the shaft 11, it is obviousthat in certain cases different gear ratios might be desired. Also, ifthe direction of rotation is critical,

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it is obvious that an idler gear between gears 22 and 23 may be providedif desired. As can be seen from FIG. 2, a lever arm 25 is suspended fromthe top of the frame 10 and a counterbalance 26 is attached thereto bymeans ofa support rod 27. A dash pot 30 is provided to damp out suddenmotion of the frame 10. The dash pot may be secured to the support forthe lathe or to the lathe itself. The dash pot is connected to the frame10 by means of a rod 31 which is secured within the frame by means of aset screw 32. FIG. 3 shows the manner in which the frame may beconnected between the centers 35 and 36 of a lathe. A support 33 for thedash pot is shown in this figure. The tool carriage slide assembly hasbeen omitted for clarity.

FIG. 4 shows the manner in which the grinding Wheel is used with theframe of FIG. 1. The grinding wheel 37, driven by a motor 38, issuspended from the supports 39 and 40 upon the tool carriage cross slideillustrated at 4-1. As can be seen from this figure, the force againstthe resistor 26 is determined almost entirely by the weight 26, and issubstantially independent of irregularities in the resistor blank 20.Different grinding forces can be obtained by adding or subtractingweight at 26.

There is thus provided a device for maintaining the grinding forcesubstantially constant while cutting a spiral groove in a resistor.

While certain specific embodiments have been described in some detail,it is obvious that numerous changes may be made without departing fromthe general principles and scope of the invention.

We claim:

1. A device for maintaining a substantially constant grinding force on aresistor during spiral grinding on a lathe to provide a spiral cuttherein, comprising: a frame; means for holding said resistor withinsaid frame; a shaft passing through said frame, adapted to be securedbetween the centers of said lathe; means for rotatably coupling saidresistor holding means to said shaft, whereby said resistor is made toturn at a speed as determined by the rotation of said shaft; meansconnected to said frame for urging said resistor toward the grindingwheel on said lathe when said frame is inserted in the lathe and meansconnected to said frame for damping out rapid changes in the position ofsaid frame during grinding.

2. A device which may be mounted in a lathe having a grinding wheel formaintaining a substantially constant grinding force on a resistor duringspiral grinding to provide a spiral cut therein, comprising: arectangular frame; a pair of chucks, supported by said frame, forsupporting said resistor within said frame; a spring, mounted betweensaid frame and one of said chucks for holding said resistor between saidchucks; a shaft, supported by said frame, adapted to be secured betweenthe centers of said lathe; means for rotatably coupling said one of saidchucks to said shaft, whereby said resistor is made to turn at a speedas determined by the rotation of said shaft; means connected to saidframe for urging said resistor toward the grinding wheel on said lathewhen said frame is inserted in the lathe and means connected to saidframe for damping out rapid changes in the position of said frame duringgrinding.

3. A device which may be mounted in a lathe having a grinding wheel formaintaining a substantially constant grinding force on a resistor duringspiral grinding of said resistor, comprising: a rectangular frame; apair of chucks, supported by said frame, for supporting said resistorwithin said frame; and spring mounted between said frame and one of saidchucks for holding said resistor between said chucks; a shaft supportedin substantially frictionless hearings in said frame, adapted to besecured between the centers of a lathe; means for providing a one to onecoupling between one of said chucks 3 Q. and said shaft, whereby saidresistor is made to turn at the same speed as said shaft; a lever armconnected to the top center portion of said frame; a counterweightsupported by said lever arm whereby said resistor is urged toward 'thegrinding wheel on a lathe when said frame is inserted in the lathe andmeans connected to said frame for damping out rapid changes in theposition of said frame during grinding.

4. A device which may be mounted in a lathe having a grinding wheel formaintaining a substantially constant grinding force on a resistor duringspiral grinding or" said resistor, comprising: a rectangular frame; apair of chucks, supported by ,said frame, for supporting said resistorwithin said frame; and spring mounted between said frame and one of saidchucks for holding said resistor between said chucks; a shaft supportedin substantially frictionless bearings in said frame, adapted to besecured between the centers of a lathe; a first spur gear on said shaft;a second spur gear connected to one of said chucks and mechanicallycoupled with said first spur gear, whereby said resistor is made to turnat a speed as determined by the rotation of said shaft; alever armconnected to the top center portion of said frame; means for supportinga weight on said lever arm, whereby said resistor is urged toward thegrinding wheel on a lathe when said frame is inserted in the lathe andmeans connected to said frame for damping out rapid changes in theposition of said frame during grinding.

5'. A method for cutting a spiral cut in a resistor on a lathe,comprising: mounting a grinding wheel with a driving means on the toolcarriage of said lathe; locating the grinding wheel below a linethrough'the turning centers of said lathe; mounting the resistorbelowvsaid line and adjacent said grinding wheel; mechanically couplingsaid resistor to a rotational driving means connected between theturning centers of said lathe; moving said tool carriage across saidresistor at a predetermined speed with respect to the rotational speedof said driving means; urging said resistor toward said grinding wheelwith a substantially constant force and damping out all rapid movementsof saidtresistor.

References Cited in the file of this patent UNITED STATES PATENTS 7

